The development of chemically recyclable polymers for sustainable 3D printing is crucial to reducing plastic waste and advancing towards a circular polymer economy. Here, we introduce a new class of polythioenones (PCTE) synthesized via Michael addition-elimination ring-opening polymerization (MAEROP) of cyclic thioenone (CTE) monomers. The designed monomers are straightforward to synthesize, scalable and highly modular, and the resulting polymers display mechanical performance superior to commodity polyolefins such as polyethylene and polypropylene. The material was successfully employed in 3D printing using fused-filament fabrication (FFF), showcasing excellent printability and mechanical recyclability. Notably, PCTE-Ph retains its tensile strength and thermal stability after multiple mechanical recycling cycles. Furthermore, PCTE-Ph can be depolymerized back to its original monomer with a 90 % yield, allowing for repolymerization and establishing a successful closed-loop life cycle, making it a sustainable alternative for additive manufacturing applications.